Abstract: A pneumatic operating device, e.g. for controlling valves, includes a cylinder (2) in which a piston (12) is movable. The piston has an axially extending rack part (11) having teeth which engage with teeth on an operating element (10) arranged in the cylinder wall (2b) for rotation transversely of the longitudinal axis of the piston and passing sealingly through said cylinder wall. The piston (12) is provided on the side opposite its rack part with a recess (24) for receiving a part of a spring (26) for the return movement of the piston. The recess (24) extends substantially into the rack part (11) of the piston, preferably through a distance of such length that it extends axially approximately up to or beyond a radial line perpendicular to the piston axis through the center of rotation of the operating element even when the piston is in a position in which the spring is compressed to its maximum.